Europe Counters Threat of Terror : Security: Despite extraordinary government measures, some lapses have already occurred.

Since the outbreak of the Gulf War, guards at the entrances to Harrods department store in London have checked shoppers for terrorist bombs. German police raided the homes of about 50 Arab nationals with possible terrorist leanings. And small tanks are guarding the Spanish airports at Madrid and Barcelona.

Meanwhile, in Belgium, a top lieutenant in the Abu Nidal terrorist organization entered the country last week on a tourist visa granted by the Foreign Ministry. After two days in Belgium, he was expelled only when a passerby recognized him and reported him to the Brussels police.

For the most part, Europe is taking seriously Iraqi President Saddam Hussein’s threat of terrorism in the countries that are battling his forces in the Gulf War.

But as the Belgian experience suggests, there have been some lapses.

“It is a most disgraceful breach of international solidarity,” said Paul Wilkinson of St. Andrews University in Scotland, a leading expert on Arab terrorism. “I can’t understand how the Belgians let such a thing happen.”

Belgian authorities have offered no explanation. A Foreign Ministry spokesman declined Wednesday to disclose more than had already become public about the case of Walid Khaled. Two top Foreign Ministry aides have already resigned, and Foreign Minister Mark Eyskens came under siege during Thursday’s debate in Parliament.

Khaled played a key role in negotiations that led two weeks ago to the exchange of four Belgians, held hostage in the Middle East since 1986, for a terrorist who was convicted 10 years ago of a grenade attack in Antwerp that left one Belgian dead.

In addition to the terrorist’s release, Khaled obtained permission to visit Belgium and meet with one of the Foreign Ministry officials who has since resigned. After Brussels police briefly detained Khaled, Prime Minister Wilfried Martens ordered his expulsion. He left the country on a plane for Switzerland the morning of Jan. 17, hours after the Gulf War began.

Otherwise, officials in Belgium and the rest of Europe have taken extraordinary counterterrorist measures. False bomb scares have been legion, and in the first such episode since the war began, two bombs exploded in Istanbul, Turkey, on Wednesday at the offices of the American Home Board and the American Bureau of Shipping.

Early today, Athens police reported explosions at two branches of U.S. and British banks in suburbs of the Greek capital. A radio station reported a third explosion, near the home of the French military attache.

Wilkinson said U.S. targets in Europe are especially inviting to Hussein’s terrorists because the United States leads the multinational force trying to drive his troops out of Kuwait.

“He has a history of practicing terror,” Wilkinson said. “ . . . We are expecting a wide scattering of attacks with varying degrees of professionalism.”

Security has been doubled and redoubled at U.S. embassies and other government installations across the Continent. Embassy officials have urged Americans to avoid gatherings easily identified as involving many of their compatriots.

Schools with heavily American student bodies closed in many European cities for the two days after the war began and reopened this week with tighter security.

U.S.-based companies have taken steps to minimize dangers. Exxon Chemical, which has plants in six European countries and sales offices in virtually all, initially banned international air travel and only as of Wednesday permitted “essential” travel.

Employees at IBM’s European headquarters in Paris have been instructed to avoid international flights. “We ask our employees to make maximum use of fax machines, telephones and video conferences,” a spokesman said. “When it is absolutely necessary for them to go somewhere, we tell them to take the train.”

European officials have generally been no less vigilant. The security ministers of the 12 European Community nations met Tuesday to assess the dangers of terrorism.

Their final communique expressed their “wish to intensify cooperation and maintain security while preserving a climate of trust necessary to a pacific cohabitation between the populations of the different communities in the member states.”

Transportation facilities are under special protection throughout the Continent. Tanks rolled out at airports not only in Spain but also in London, Rome and Naples. Security guards open coin-operated lockers daily at French train stations to check for bombs. At Germany’s biggest airport, in Frankfurt, luggage is routinely X-rayed three times, passenger identification is more carefully checked, and authorities may confiscate any electronic equipment.

Security measures are disrupting the daily routines of millions. In London, one or two subway stations have been closed for an hour or two almost daily, often after police identified “suspicious packages” that turned out to be harmless.

Morning rush hour has become even worse than usual in Paris, where commuters must compete with 30 squadrons of 85 mobile gendarmes each.

France, where 13 people were killed and more than 250 injured during 10 months of terrorist bombings in 1985 and 1986, appears now among the most nervous of the European countries.

Altogether, 200,000 special police, including some military security officers, are guarding France’s 55 nuclear power plants and other major industrial sites.

Germany, where 260,000 U.S. military personnel are stationed, is no less anxious about the terrorism threat. The Bonn government expelled 28 Iraqi diplomats Thursday, ordering them to leave within four days.

“The government does not feel it appropriate for Iraq to maintain such a high diplomatic presence in the current situation, especially since there are no German or other Western diplomats left in Baghdad,” a Foreign Ministry spokesman said.

Last week, police raided the homes of 50 Arab nationals throughout the country and detained four who were suspected as potential terrorists. The four, who had entered the country on false travel papers, were sent back to the Mideast.

“We’ve prepared ourselves for weeks for this situation,” said Hans Neusel, who as state secretary in the German Interior Ministry is primarily responsible for anti-terrorist measures. “We have to take Saddam Hussein’s threats seriously that . . . terrorist attacks will be attempted on a global scale.”

U.S. servicemen are lying low, to the consternation of Harry Hu, owner of the Green Goose Discothek, a GI haunt in Wurzburg. Hu says he gets 15 to 20 customers a night, a fraction of the 400 to 500 he used to be able to expect on weekends.

“Our business is totally dead,” he said. “I won’t be able to hang on very much longer.”

In Spain, Prime Minister Felipe Gonzalez told reporters that he is more concerned about terrorism than about the safety of sailors aboard the three Spanish warships in the Persian Gulf.

Havemann reported from Brussels and Marshall from Bonn. Staff writers Rone Tempest in Paris and Stanley Meisler in Barcelona also contributed.